According to Huijser, the US was less inclined than his native Netherlands – and “just about everywhere else I’ve worked” – to see conservation as a destination for crossings. But that is changing. The Infrastructure Investments and Jobs Act, which went into effect in November and has earmarked $350 million for wildlife crossings over the next five years, provides new federal funding for projects and research to reduce wildlife-vehicle collisions and fragmented areas to connect the habitat. Although that amount represents just 0.3% of the $110 billion road bill budget, road ecologists have hailed it as a landmark investment. There is now a publicly funded way to build crossings that target conservation goals, although reducing collisions remains the primary focus, says Rob Ament, senior conservationist at the Center for Large Landscape Conservation. The targeted funding also means wildlife crossings are no longer competing with potholes for scarce tax dollars. “I think it’s actually a big step forward,” says Ament. The bill recognizes that we need to design infrastructure “taking into account both things: the needs of people – the movement of goods and people – but also the movement of wildlife,” he says. “And finally we do.”
But build what? North America’s most influential examples of hybrids are along the Rocky Mountain Front in Canada. The area with the greatest diversity of large mammals on the continent is bisected by the Trans-Canada Highway. A series of 44 wildlife crossings (six overpasses and 38 underpasses) were built in Banff National Park to bridge the gap and create a connected system used by a variety of species including moose, cougar and coyote, and rarer animals such as red fox , grizzly bears, wolves, wolverines, snakes, beavers and lynxes.
But Banff’s wild animal crossbreeds, like most, suffer from a kind of Horseless Carriage Syndrome, their design constrained by existing infrastructure. Tunnels are often poorly adapted culverts, the (usually concrete) tubes that carry water under roads. And flyovers have generally taken over from roads — they’re built to look like they’ll support the weight of an 18-wheeler and then “top-dressed” with foliage, Lister says.
A variety of experiments are beginning to reconsider this model. One is the Wallis Annenberg Wildlife Crossing, the $90 million wildlife bridge under construction just north of Los Angeles. Designed by architect Robert Rock, it eschews the humped arches of older bridges in favor of a vast flat surface that only needs a pillar to support it between mountains and across a highway that an estimated 300,000 cars cross each day. It’s the “poster child of innovation,” says Renee Callahan, chief executive of ARC Solutions, a group researching how to build better wildlife bridges. “It’s literally designed for species from mountain lions to mule deer to deer mice,” says Callahan. “They design it all the way down — literally down to the mycorrhizal layer, in relation to the soil, to make sure the soil itself has the fungal network that can support the native vegetation.”
There are many unknowns as construction begins, not the least of which is how different species will respond to the sheer volume of vehicles passing underneath. The National Park Service will monitor activity on the bridge as well as DNA profiles of animals on both sides of the highway. Many are watching what will happen to the region’s mountain lion population. Over time, inbreeding has resulted in genetic abnormalities, such as a tell-tale kink in native cats’ tails. The agency predicted that without crossing, the population would become extinct within decades.
Across the US, the $350 million Infrastructure Act falls far short of what is needed to deal with the fragmentation caused by the nation’s 4 million miles of public highways. But there are a handful of innovations that could tip the cost-benefit analysis by allowing intersections to be built at a lower cost or in places where it wasn’t previously feasible.
Animal bridges are currently only built where there is protected land on either side of the road, as the typical cost of building a concrete bridge on a site that may be developed in a few years would be difficult to justify. Lighter, cheaper modular systems could be deployed in places where the future is less certain, Huijser explains: “If the adjacent land becomes unsuitable for wildlife, we take it apart and you can move it.”
One possible material for such modular systems is precast concrete. Also attracting attention is fiber-reinforced polymer (FRP), a material less dense than concrete made from structural fibers embedded in resin. FRP has been used to build foot and cycle bridges in Europe and a quick and easy wildlife bridge in Rhenen, south of the Gooi in the Netherlands. Currently, the Federal Highway Administration does not allow its use on transportation infrastructure in the United States, but there are growing calls for changes. “These are obstacles that are mainly related to politics and governance. It’s not about science and it’s not about technology,” says Lister.
